Dart stream .asBroadcastStream memory leak

Question

In our Flutter application we have memory leaks and streams not being closed. We traced the source to code such as:

Rx.combineLatest(...).asBroadcastStream()

The result of RxDart .combineLatest() is a single-subscription stream. Adding .asBroadcastStream() makes the stream conveniently available to our various Flutter displays. However when these displays are closed the streams being combined are still active.

Answer 1

From the .asBroadcastStream() documentation:

The returned stream will subscribe to this stream when its first subscriber is added, and will stay subscribed until this stream ends, or a callback cancels the subscription.

So by design the stream exists until explicitly cancelled. To cancel the subscription when the last listener cancels use:

Rx.combineLatest(...).asBroadcastStream( onCancel: (sub) => sub.cancel() )

There is further discussion in Stream.asBroadcastStream - Easy to cause leaks, what is the rationale? #26686